Emamy Hamed, Gang Oleg, Starr Francis W
Department of Physics, Wesleyan University, Middletown, CT 06459, USA.
Department of Chemical Engineering, and Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA.
Nanomaterials (Basel). 2019 Apr 26;9(5):661. doi: 10.3390/nano9050661.
The functionalization of nanoparticles (NPs) with DNA has proven to be an effective strategy for self-assembly of NPs into superlattices with a broad range of lattice symmetries. By combining this strategy with the DNA origami approach, the possible lattice structures have been expanded to include the cubic diamond lattice. This symmetry is of particular interest, both due to the inherent synthesis challenges, as well as the potential valuable optical properties, including a complete band-gap. Using these lattices in functional devices requires a robust and stable lattice. Here, we use molecular simulations to investigate how NP size and DNA stiffness affect the structure, stability, and crystallite shape of NP superlattices with diamond symmetry. We use the Wulff construction method to predict the equilibrium crystallite shape of the cubic diamond lattice. We find that, due to reorientation of surface particles, it is possible to create bonds at the surface with dangling DNA links on the interior, thereby reducing surface energy. Consequently, the crystallite shape depends on the degree to which such surface reorientation is possible, which is sensitive to DNA stiffness. Further, we determine dependence of the lattice stability on NP size and DNA stiffness by evaluating relative Gibbs free energy. We find that the free energy is dominated by the entropic component. Increasing NP size or DNA stiffness increases free energy, and thus decreases the relative stability of lattices. On the other hand, increasing DNA stiffness results in a more precisely defined lattice structure. Thus, there is a trade off between structure and stability of the lattice. Our findings should assist experimental design for controlling lattice stability and crystallite shape.
用DNA对纳米颗粒（NPs）进行功能化已被证明是一种将NPs自组装成具有广泛晶格对称性的超晶格的有效策略。通过将该策略与DNA折纸方法相结合，可能的晶格结构已扩展到包括立方金刚石晶格。这种对称性特别受关注，这既是由于其固有的合成挑战，也是由于其潜在的有价值的光学特性，包括完整的带隙。在功能器件中使用这些晶格需要一个坚固且稳定的晶格。在这里，我们使用分子模拟来研究NP尺寸和DNA刚度如何影响具有金刚石对称性的NP超晶格的结构、稳定性和微晶形状。我们使用Wulff构造方法来预测立方金刚石晶格的平衡微晶形状。我们发现，由于表面粒子的重新定向，有可能在表面与内部带有悬空DNA链的粒子形成键，从而降低表面能。因此，微晶形状取决于这种表面重新定向的可能性程度，而这对DNA刚度很敏感。此外，我们通过评估相对吉布斯自由能来确定晶格稳定性对NP尺寸和DNA刚度的依赖性。我们发现自由能主要由熵分量主导。增加NP尺寸或DNA刚度会增加自由能，从而降低晶格的相对稳定性。另一方面，增加DNA刚度会导致晶格结构定义得更精确。因此，在晶格的结构和稳定性之间存在权衡。我们的发现应有助于控制晶格稳定性和微晶形状的实验设计。
